[Les Cargill[_4_]]

(Don Pearce) wrote:
On Sun, 18 Jan 2015 21:38:47 -0600, Les Cargill
wrote:

Peter Larsen wrote:
"Les Cargill" skrev i en meddelelse
...

Between the 1x ( 0.525 cu ft ) box and the 2x ( 1.05 cu ft ) box, there
is one hump in the group delay that goes from 4ish to 8ish msec, around
75-80 Hz in the frequency response.

In winisd you can fix any parameter and then see what happens to the design,
so in case the port lenght is silly you try another area. If you err, then
err to the side of the too long a port because the bass units Fs will get a
wee bit lower in use. Do not err to the side of the too high tuning because
it will give a "loose" sound with flappy transients.


Interesting. I was concerned that too long a port would fight the box.
Still; moving from 20.00 to 1.97 inches diameter ( from 50.8 to 20.038
mm ) seems rather hairsplitting That gets it to a length of 0.75 inches.

Since the ideal front design is 14"x14" for a steel guitar speaker,
there was hardly room for a pair of 2" ports.

They'd just have to go in back.

Oh, that btw. is the answer to whether a slightly too short port is OK, no,
it is not redesign so that you have more length and lower air speed in port
or make it a bit smaller. I didn't think that mattered so much until
Quali-Fi service here in Denmark suggested that I should double the port
area since I had room for longer ports, it was a surprising sonic
improvement, unexpected because of my generally modest playback spl.


huh. That actually makes sense.

Doubling the box nearly has to be more of a perturbation than 1.25 mm of
port depth.

But then again, ports are critically sensitive elements. Still, I am
skeptical that "just take it outside and measure it" is going to
allow enough accuracy to be able to tell.

Measure the impedance curve, what sounds well to me is the setups where the
lower impedance hump is equal to the higher one or larger, ie. generally
systems that are tuned lower than optimally linear.


True enough.

(btw, this is not for me; it's for another participant on a different
forum who has a speaker and is fishing for box designs ).

But, surely, in fishing putting some bait on the hook, such as telling us
what unit and what its parameters are may increase the chance for a good
catch.


It's an Eminence EPS-12C. I guessed ( incorrectly ) that this didn't
matter It's not a bass driver at all; it's a guitar speaker. Fs is
49.17 Hz. I get the feeling it's really designed for infinite baffle.

http://www.usspeaker.com/Eps12c-1.htm

The gentleman will use it for pedal steel, presumably with a lowest note
of C2 ( 69.4 cycles ).



Les Cargill

Kind regards

Peter Larsen





I was going to ask. Why are you porting this at all?

I don't know exactly. I suppose he wants a little more bass support.
Steel goes lower than 6 string.

Bottom E on a
guitar is 82Hz, and the speaker cone is far better protected and
supported in an IB box.


Agreed.

Vox get away with open backs because their amplifiers are relatively
low power compared to the speaker drivers. And they leave the backs
open deliberately to roll off the bass for a cleaner sound.

d



--
Les Cargill